diff --git a/mlatom/data.py b/mlatom/data.py
index e110381..7df46cc 100644
--- a/mlatom/data.py
+++ b/mlatom/data.py
@@ -1322,7 +1322,7 @@ def excitation_energies(self, excitation_energies=None):
 
 
     @property 
-    def nstates(self) -> np.int:
+    def nstates(self) -> int:
         '''
         The number of electronic states.
         '''